As Charlene already posted for me the Slaty-backed Gull and Glaucous-winged
Gull were both present this morning at Carlyle Lake (Clinton Co., IL). Dan
K. had the Slaty-backed in view when I pulled up. We watched the
Slaty-backed Gull sitting and flying just over the water from the Saddleback
dam for the next hour. It provided great views as it was less than 150
yards out for much of our viewing time. Eventually we moved just a bit
north to the parking lot with the boat ramp and could see the Slaty-backed
as we looked south. Also had at least 4 Purple Finches and 1 American Pipit
fly over while there.

I got some pictures which can be seen at the below link. None are
exceptional, but the key fieldmarks can be seen along with one picture that
is in direct comparison with a Lesser Black-backed Gull.
Hopefully the following link works....